1. Field of the Invention
The present invention relates to a method of detecting cut-off calls in a switching system, and more particularly to a method of detecting cut-off calls occurring in a switching system by using a control memory.
2. Background of the Related Art
Generally, a switching system must use a switching device in order to connect or disconnect a call. Switching devices may be classified as one of two types: (a) time switch that exchanges two time slots on the same data stream and (b) space switch that exchanges the same time slots on different data streams.
A component that causes a switching device to be connected or disconnected is a control memory provided in the switching device. If data needed for call connection and release are recorded in the control memory within the switching device, the connection of the switching device may be established or released.
FIG. 1 illustrates the structure of a processor for controlling a time switch in the related art, wherein a Subscriber Service Device Processor (SSDP) (20) handles a control memory (15) in order to connect or disconnect a time switch (10).
FIG. 2 illustrates the structure of a processor controlling a space switch in the related art, wherein a Switch Network Device Processor (SNDP) (50) handles a control memory (45) in order to connect or disconnect a space switch (40).
A Code Division Multiple Access (CDMA)-2000 system, including both the time switch (10) and the space switch (40), comprises SSDP (20) that connects or disconnects the time switch (10) by handling the control memory (15) provided in the time switch (10) and SNDP (50) that connects or disconnects the space switch (40) by handling the control memory (45) provided in the space switch (40).
Further, an International Mobile Telecommunication (IMT)-2000 which includes a time switch for connection with a Public Switched Telephone Network (PSTN) or an Integrated Services Digital Network (ISDN), comprises SSDP (20) that connects or disconnects the time switch (10) by handling the control memory (15) provided in the time switch (10).
While a call is connected using the control memory, a cut-off of the call may occur as a result of a sudden disconnection of the call. A call cut-off may also occur at various parts of a switching system, but mostly it occurs at switching devices such as a time switch and a space switch.
FIG. 3 is a flow chart illustrating the process of connecting or disconnecting a call in a switching system of the related art. If a call connection is requested, SSDP (20) or SNDP (50), searches for an idle area of the control memory (15 or 45) provided in the switch and formats the data needed for call connection in a form which is appropriate for recording in the control memory (15 or 45) of the time switch (10) or the space switch (40) (S10, S12, S14). Then, the call is connected by recording the data of the form formatted at step S14 in the idle area of the control memory for which is searched at step S12 (S16).
Thereafter, if it is intended to finish the conversation and disconnect the call, SSDP (20) or SNDP (50), according to a call release request, searches for an idle area of the control memory (15 or 45) provided in the time switch (10) or the space switch (40). SSDP or SNDP then formats the data needed for call release in a form which is appropriate for recording in the control memory (15 or 45) of the time switch (10) or the space switch (40), in order to disconnect the time switch (10) or the space switch (40) (S18, S20, S22). The call is then disconnected by recording the data of the form formatted at step 22 in the idle area of the control memory searched at step S20 (S24).
As described above, SSDP (20) or SNDP (50) which controls the control memory (15 or 45) needed for the call connection, performs simply the function of call connection and release. If a failure occurs at the time switch (10) or the space switch (40) while a call is connected (in other words, if the system clock is unstable or the time switch (10) or the space switch (40) has poor quality), a cut-off call may occur, which could result in an abrupt disconnection of the call.
The switching system of the related art is disadvantageous because it does not perform the function of detecting calls which have been cut-off. The inability to perform this function has caused problems, not the least of which include a deterioration in reliability of the system. These drawbacks have also made repair and maintenance of the system difficult.